This invention relates to vehicle axles and axle subassemblies, and particularly to trail arm twist beam axles and axle subassemblies.
A trail arm twist beam axle is intended to semi-isolate one wheel of a vehicle such as an automobile from the opposite wheel. Connection points are made to the body mounts, wheel spindles, shocks and springs, as well as to track bars for lateral stability. Individual component pieces typically making up an axle assembly include the twist beam, trail arms, flanges, spring supports, jounce bumpers, shock mounts, bushing mounts and torsion bar.
Various cross sectional configurations have been suggested for twist beam and torsion bar elements heretofore, although typically a twist beam comprises an inverted, U-shaped beam for bending loads, coupled with a separate solid torsion rod of different material and characteristics from those of the beam, and extending through the open central portion of the beam, for accommodating torsional loads. The U-shaped beam is normally a drawn or stamped member which is not particularly strong in torsion. Both ends are attached to stubs extending in from the spring seats. The separate rod to control torsional loads is specially fabricated of a high strength steel. Its ends are attached separately from, and in a special relationship relative to, the ends of the beam. The material costs, manufacturing costs and assembly costs of the two-piece twist beam and torsion bar arrangement are significant. Some very light weight automobiles are capable of using the beam without a torsion bar, but the torsion bar is included if the vehicle is expected to carry any significant load, is a heavier-type vehicle, or is to have quality handling characteristics.
In the prior patent applications identified above, employees of the assignor herein disclosed a specially constructed twist beam axle free of the necessity of a customary torsion bar which adds weight and cost, but having excellent torsional strength. In the above-identified U.S. Pat. No. 5,324,073 is set forth a tuned twist beam axle allowing axles to have a variety of good torsional characteristics to suit the style and nature of the vehicle involved.
In all of these axles set forth in the above-related applications, torsional stress applied to the structures has been found to cause certain complex movements to occur in the axle portions. Specifically, under torsion, i.e., where the two ends of the axle are twisted in opposite rotary directions, the two legs and the two loops on the legs of the axle not only tend to move toward each other transverse to the axle axis, but also tend to move in opposite directions to each other parallel to the axle axis. The torsional stresses and these resulting complex movements are illustrated by the arrows in FIG. 6. The stress to the axle caused by these movements is greatest at the axle mounting to the spring pods, at the opposite ends of the axle, and decreases from these locations, toward the central portion of the axle. The goal of the present invention is to alleviate these axle end stresses with a special axle structure.